In the design of portable radio equipment, and in particular personal paging devices, size is an extremely important factor. Many previous paging devices employed relatively large receive antennas, thereby significantly increasing overall device dimensions. Antennas of this scale were generally required as a consequence of the use of relatively low RF paging frequencies, and also so as to ensure adequate reception of the paging signals. Specifically, high antenna gain is desirable, and under certain conditions may in fact be necessary to ensure achievement of full receiver range capability. However, size constraints preclude incorporation of conventional high gain antenna configurations into paging receivers designed to be relatively compact.
The large size of many conventional paging receivers has required that they be mounted on the side of the body, usually through attachment to the belt or through placement in a pocket. Recently, however, it has been desired to realize paging devices sufficiently compact to be, for example, worn on the wrist. One advantage offered by wrist-carried paging receivers is that they may be held in front of the face, thereby facilitating viewing or adjustment by the user.
Existing wrist-carried paging receivers often include simple loop type antennas responsive to the magnetic field component of the RF signal. In such antennas the loop element is generally disposed within the wrist band of the user. Although this type of antenna system has tended to provide only marginal performance, it enables the loop antenna to be concealed within the wrist band housing. However, this arrangement is of advantage only if it is desired that the attachment mechanism consist of a wrist band or other loop-type device. Accordingly, it would be desirable to provide an antenna system which is capable of being implemented within a paging receiver of compact dimension, and which does not presuppose a particular type of attachment mechanism.
As noted above, receive antennas incorporated within conventional terrestrial paging devices have tended to be somewhat large, partially as a consequence of the use of relatively low paging frequencies (e.g., &lt;1 GHz). However, existing satellite communications systems operative at, for example, 1.5 or 2.5 GHz, afford the opportunity for paging receiver antennas of smaller scale. Antennas operative at these frequencies would need to have gains sufficiently low to project broad radiation patterns, thus enabling reception of paging signals from a broad range of angles. This is required since terrestrial deception of satellite signals is based not only upon line-of-sight transmissions, but also upon transmissions scattered and reflected by objects such as buildings, roads, and the like. Hence, it is an object of the present invention to provide a compact antenna capable of receiving paging signals from communication satellites.